The invention relates to carbide tipped bandsaw blades used for cutting metal, and to a method of making bandsaw blades.
Prior to the advent of carbide-tipped bandsaw blades, it had been conventional to form bandsaw blades as so-called bi-metallic blades comprised of a spring steel alloy body to which a high speed steel strip was electron beam welded. A back edge of the body was usually beveled along its opposite corners by means of a cutting operation performed on an edging machine, in order to minimize stress concentrations. Cutting teeth were formed directly in the high speed steel strip by a milling operation. Hence, the transverse width of each tooth equaled the thickness of the band. If desired, some of the teeth could be bent so as to be offset toward opposite sides of the band.
After the teeth were formed, it was been common to grit blast the sides of the blade for cleaning purposes, and/or to grit blast the front edge of the blade to hone or clean the teeth. During a cutting operation, the teeth would wear out, and the body of the band would be subjected to fatigue stress. Because of the heavy stresses imposed on the teeth when entering or leaving a metal workpiece, the teeth would wear relatively rapidly, and the life of the blade (usually less than 100,000 revolutions in a cutting machine) was determined by the wear rate of the teeth. The worn out teeth of such blades were normally not subjected to resharpening operations. Therefore, little emphasis was placed on increasing the fatigue life of the band body, due to the fact that the overall life of the blade itself could not be extended beyond the time when the teeth wore out.
This situation has been changed by the introduction of carbide-tipped bandsaw blades in which carbide cutting tips are brazed onto a small concave surface at an extremity of a tooth portion of the steel and, e.g., see U.S. Pat. Nos. 2,826,941; 3,104,562; 3,788,182; and 4,784,033. The last-named patent further discloses that the inclusion of a ductile metal foil in the braze layer enables the braze joint to accommodate limited deformation, thus allowing the use of large carbide tips on metal bandsaws.
The carbide tips are highly wear resistant and can be resharpened, whereby the life of the carbide tips is extended. However, such extended tip life may be of little benefit if the fatigue life of the blade is considerably shorter than the tip life. Accordingly, it would be beneficial to increase the fatigue life of a carbide-tipped bandsaw blade.
The fatigue failure of the blade results from the twisting and bending of the blade. For example, as the blade travels around the guide wheels of a bandsaw machine, the front cutting edge of the blade bends and is thus subjected to tensile stresses which are directly proportional to the radius of curvature of the guide wheels. The tooth portions of the blade, which include the carbide tips, have a higher degree of flexural stiffness than the gullet portions of the band which separate the teeth. Hence, the primary blade deformation and resulting tensile stresses occur primarily in the gullets, especially at the deepest point of the gullet.
It has been proposed to minimize the stress concentrations in the gullet regions of a bandsaw blade by spacing the deepest point of the gullet longitudinally forwardly of the topmost point of a drilling carbide tip by a distance equal to at least 15% of the pitch of the teeth, and by arranging that deepest point to lie on a curved section of a bottom of the gullet. The curved section, which is defined by a radius of curvature larger than the largest depth of the gullet extends forwardly and rearwardly of the deepest point by longitudinal forward and rearward distances, respectively. Each of the forward and rearward distances is equal to at least 10% of the pitch of the teeth. Notwithstanding the improved fatigue life produced by such a bandsaw blade, it would be further desirable to yet further extend the fatigue life.